Grinding method and apparatus



May 26, 1931. G. H. CARNAHAN GRINDING METHOD AND APPARATUS Filed-Sept. 29. 192s Q WA/%////\w magi this purpose. In order that the flint Patented May 23, 193 1 GEORGE HOLMES CABNAH AN, OF NEW YORK, N. Y.,

IEN'I'S, '10 RUBBER SUBIAOERS, INC OF WILMINGTON,

T1011 01' DELAWARE ASSIGNOR, BY 11mm ASSIGN- DELAWARE, .L comm- G RINDING METHOD AND APPARATUS Application filed September 28, 1928. Serial No. 809,388.

This invention relates to improvements in grinding methods and apparatus, and more particularly to improvements in grinding operations carried out in ball mills or tube mills.

In grinding operations heretofore carried out in ball mills or tube mills, hard surfaced grinding media have been employed, and flint pebbles have been extensively employed for pebbles 0 may have suflicient weight to be effective, the pebbles employed are relatively large, around three inches in diameter. Iron or other metal balls have been employed in some cases, but their application is limited, and they cannot 5 be employed when the materials being ground are corrosive or act upon the metal, nor can they be employed Where metallic contamination resulting from the abrading of the metal balls must be avoided. Such balls, whether 0 of metal or of flint, have hard grinding surfaces and are in contact with each other only at isolated points, and since the grinding action is primarily a surface action, the grinding is for the most part limited to the several 5 points of contact between the abrasive pebbles or balls. The present invention provides an improved method of grinding in which the grinding media have resilient surfaces so that 0 adjacent balls will have a substantial surface contact with each other. The grinding media which I employ have a resilient rubber sur-' face but have a sufficient weight and density to accomplish the necessary grinding action.

Where the rubber balls employed as grinding media, according to the present invention, are not required to have a s ecific gravity materially greater than that o flint, the balls may be made up entirely of a rubber composition containing a relatively large amount of a heavy filler compounded therewith, such as litharge, so that the rubber compound, when vulcanized, will have a specific gravity of around 2.6 or greater. By using a heavy filling material like litharge in sufiicient amount, a specific gravity can be increased to around 3 or in some cases even more without seriously afiecting the wearing qualities of the vulcanized rubber com osition. The rubher composition employe should have high abrasive resisting pro erties, particularly at its outer wearing 'sur aces. It is not so important to have the center of solid rubber alls so resistant, and in some cases the balls may be of a composite character, with aheavy rubber composition in the center, and with a special composition on the exterior capable of withstanding the necessary wear and abrasion. Compositions of the nature of tread stocks for automobile tires are well suited for use for the outsides of such balls, but in order to impart to the balls a suflicient specific gravity, it is important for a suflicient amount of a heavy filler like litharge to be incorporated in the rubber before it is vulcanized. 4

Instead of employing balls made entirely of rubber composition, it is more advantageous to employ balls with metal centers and with the rubber covering surrounding the same. The metal centers may be made of different metals but a specially high specific gravity can be obtained by using a metal made up of about 90% lead and 10% antimony and which has a specific gravity of around 10.9. The hardening effect of the antimony on the lead will prevent distortion of the metal core. Such metal cores will be covered with a layer of rubber which may be for example, about or inch in thickness. The rubber coating will be ap plied to the metal cores and vulcanized thereon to form an integral ball structure. For this purpose, a tough rubber compound should be employed, such as is employed in the threads of automobile tires, and which will be capable of withstanding prolonged use for grinding purposes.

Instead of making the balls or rods of uniform size, they are more advantageously made of diflerent sizes in order to induce a differential or rubbing efiect between balls or rods of different sizes in the operation of the ball mill or rod mill. The metal cores may, for example, be cast in at least three different diameters, and then coated with the rubber casing of tou h rubber, for example, of or inch in t ickness. If, for example, the cores are cast of diameters of 1 inch, 1 1 inches and 1% inches "and if a layer of tough rubber compound of approximately A inch is applied thereto, the'diameter of the finished alls would be increased by 4 inch each by the rubber coating, of 1% inches, 1 inches and 1% eter respectively.

The specific gravity of the rubber coating ma be, for example, around 1.45, but the bal as a whole will still have a radically higher specific gravity than that of flint pe bles, for example, around 6, or about 2 times the specific gravity of flint. It will be evident that the specific ravity of the ball as a Whole will vary wit the thickness of the rubber layer and the diameter of the metal core, and also with the composition of the metal core.

In employing such grinding media and in carrying out the grinding operation therewith, ball mills or tube mills such as are commonly em loyed with flint pebbles may be employed, ut with the flint pebbles replaced by the new grindin media. The ball mills may thus be metal iall mills with a lining which may be a metallic lining or a silex or porcelain linin or a rubber lining. The use of rubber line mills has important advantages for certain purposes, but the present invention, in its broader aspects, includes the use of mills of various kinds and with linings of different materials.

In the carrying out of the rinding operation with many materials, t e employment of the inding media of the present invention, with their resilient surfaces, have important advantages. Instead of presenting only a point of contact with each other, as in the case of grinding balls with hard surfaces, the rindin balls of thepresent invention are attene somewhat where they come in contact with each other, because of the resilient character of the rubber coating or of the heavy rubber ball employed. This flattenin of the rubber surfaces under pressure and superimposed weight provides substantial working areas between the adjacent balls, so that the working area which is accomplishing the grinding is vastly increased. Rubber giving balls inches diam- Working against rubber does not slide with ease, and therefore the action is somewhat more of a tearing action than a pounding action. The tearing apart of the structure of the materials being ground is induced not only by the pulling friction between the rubber surfaces but also by the differential surface speeds where the balls are of difierent diameter.

The greatly increased density of the balls, where a metal core is employed, enables smaller balls to be employed. The smaller balls have a greatly increased surface for an equal volume of charge, but their units of weight are nevertheless sufficiently great to be effective.

Accordingly, with the new grinding media, there can be obtained a greatly increased grinding action, due to the greatly increased area of contact between the balls, to the enhanced friction between the balls, and the increased area of surface of the balls for a given volume, because of their smaller size and their greater weight. The balls can be employed in mills of the present diameter and speed but advantage may be taken of their greater area, the1r smaller size, and their greater effectiveness per unit volume by employing them in mills of lesser diameter. With the new grinding media, employed in mills of the size now emplo ed, a greatly increased grinding effect can b e obtained, as compared with the use of flint pebbles; while the same grinding effect can be obtained in a mill of smaller size.

The employment of mills of smaller size, with the new grinding media, enables substantial economies to be obtained in power costs of the grinding operation. The horse power expended in driving revolvin ball mills increases as the square of the radlus, so that smaller mills can be operated at substantially less power cost than larger mills.

The grinding operation of the present invention is further promoted by the greater specific gravity of the grinding balls employed, and the greater effective weight of the balls. For example, in grinding wet materials where the balls are submerged in water, the effective weight of the balls is only the difference between the weight of the balls and the Weight of an equal volume of Water. With flint pebbles, the effective difference in specific gravity is only about 1.5 as against 5 or 6 in the case of the heavy rubber covered balls of the present invention.

In carrying out the grinding operation, the materials to be ground can be charged into the mill, and the ground material discharged therefrom, in much the same manner as at present with mills employing flint pebbles; and the grinding operation can be regulated by regulating the flow and to some extent by the speed of operation, etc. The rate at which the mill is revolved should be such as to prevent slippage. Slippage between the walls of the mill and the grinding media can be elimi nated by suitably adjusting the peripheral speed of the mill.

The resilient rubber surface greatly increases the area of contact between lining and balls, thus permitting a reduction in peripheral speed without slippage with corresponding saving of power.

he improved grinding process of the present invention is of more or less general application for grinding operations where the material to be ground does not require hard grinding surfaces. The process can thus be employed for grinding vegetative material where it is desired for any reason to rupture the individual cells and destroy or break down the cellular or fibrous strucnee-aces A particularly .valuable application of the process is in the production andtreatment of wood pulp and other fibrous pulps. -Wood which has been softened by treatment with steam or with chemicals which soften the inter-fibrous ingredients so that the softened chi s can then be ground or disintegrated to orm a fibrous pulp, can advantageously be subjected to such grinding and pulping operation by the improved'process of the present invention. Partially cooked wood pulp or wood chips, with the individual fibres still connected with softened cementing materials can be further disintegrated and ground and converted into a pulp by grinding according to the improved process of the present invention. Even where the pulp has been produced by the chemical, cooking of wood or other material, the resulting cooked chips or pulp can be subjected to a further refining treatment by subjecting the same to further grinding with the'improved grinding media and apparatus and according to the improved process of the present invention. This further grinding operation may replace, in whole or in part, the further refining to which pulp is now subjected in heaters or in Jordan mills, or both. The action 0 the rubber surfaces ofthe balls u n the ferential surface speeds of the balls, the pulling friction between the rubber surfaces. is increased, and an increased tearingapart of the plant structure is induced. The vegetable material is moreover subjected to suflicient pressure, combined with the tearing and friction to reduce the material to a disintegrated con ition, without, however, injuring the material to any such extent as might be caused ."by the employment of grinding balls with hard wearing surfaces.

The employment of the balls with rubber surfaces has the further im ortant advantage of preventing contamination ofthe ound material by articles'of metal orof int. Abraded meta or .sand or slimes from the abraded flint rock can be eliminated. It is evident that the rubber compound employed should be one which is resistant to the action of whatever liquid may be present admixed with the material being ground; and that where the material acts too injurious'ly upon the rubber surfaces, material cannot to advantage be ground according to the resent process.

e improved grinding process of the present invention can be a plied for other purposes such as the in ing of vegetable ma terials for the 'pro notion of drugs, or the extraction of drugs, or the disintegration or extraction of various materials which re-v quire a grinding operation. So also, vegetable materials such as starch, etc. which must be prepared in a finely divided state 'can advantageously be gro und by the present process. Slimes or colloidal sus nsions can" also be readily prepared; and 'fierent materials can be admixed with each other during the grinding operation, for example, yeast or bacteria can be ground with starch to produce a material well adapted for use for fermentation purposes.

Decortication can also be carried out according to the present process, for example, where it is desirable to remove an outer covering which is'much softer than a harder interior woody structure.

The present process is particularly advantageous in its application to the extraction of ru her from rubber bearing plants such as the guayule plant, but this process is more specifically described and claimed in my companion application, Serial No. 309,364, filed of even date.

An apparatus adapted for the practice of the present process is shown in the accompanying drawings, the ball mill or tube mill itself being shown conventionally, with a conventional inlet and outlet. It will be evident that the ball mill or tube millmay be of difierent sizes and dimensions and may have suitable inlet and outlet connections which will differ somewhat with the different materials being ground or disintegrated therein.

In the accompanying drawings Fig. 1 shows the mill with part of the shell cut away, and Fig. 2 shows three rubber cov- 11-.

ered balls in central section pressed against each other.

The drum 1 of the ball mill or tube mill is supported by suitable standards or supports 2 and has an inlet 3 and outlet 4, shown 12;

conventionally, the outlet discharging into a spout'5. The mill is rotated in the usual way, as-by a gear 6, and a cooperating drivin car (not shown).

lthin the ball mill or tube mill is a 1:!

charge of rubber covered balls, as shown conventionally in Fig. 1 where part of the shell of the drum is cut away. Three of the balls are shown in pencil cross-section in Fig. 2. each ball being made up of a core 7 of dense heavy metal with resilient rubber surfaces or layers 8 of substantial thickness surrounding the heavy metal cores. The three balls shown in Fig. 2 have a substantial area of contact with each other as indicated at 9, this flattened area of contact varying in practice with the pressure exerted by the balls against each other.

In the operation of the mill and the carryin out of the process, the rotation of the mill wi 1 cause the balls to be raised and to roll or fall down over each other, and, where the balls impact against each other, or where the are forced together by the weight of the bal s, they will have flattened surfaces, which flattened surfaces will, however, continually change with the rotation of the mill and the changed positions of the balls. The material undergoing grinding or disintegration will be subjected to the grinding and disintegrating action of the flattened surfaces which are of a resilient character and which have a very substantial area, as compared with the very limited area of contact of metal or other non-resilient balls.

It will thus be seen that the present invention provides an improved grinding proces in which the grinding operation is carried out with media having resilient rubber surfaces, but having a suflicient density to enable efl'ective grinding to be obtained. It will further be seen that the grinding operation with such grinding media has important advantages, such as the greatly increased surface contact between the adjacent balls, the

increased tearing action which such increased surfaces impart, and which is further improved by the differential action of balls of different sizes, etc. From the apparatus standpoint, it will be seen that the invention provides new inding media both in the form of heavy soli rubber balls, and heavy metal balls provided with rubber coverin and that these balls can be made much sma ler in size than flint pebbles, particularly in the case of the metal balls with rubber covering, with resulting advantage in the cost of operation and in the size 0 grinding mills required. The new grinding media itself also forms a part of the invention, as well as the grindin mills in which such media is employed an the improved grinding process carried out therewith. V

I claim: 1. The improved method of grinding or disinte ating materials in ball mills or tube mills wi ich comprises subjecting the same to the action of grinding balls having resilient rubber wearing surfaces which flatten under pressure where the balls come into contact with each other, the resilient surfaces of said balls being of substantial thickness and the heavy metal core being of suflicient weight to cause the balls to flatten where they come in contact with each other during the grinding operation, whereby the resilient surfaces have substantial surface areas in contact with each other during the grinding o ration.

2 The improved metho of grinding or dislntegrating materials in ball mills or tube mills which comprises subjectin the same to the action of grinding media made up of balls havi n a resilient rubber wearing surface and having a dense core of heavy metal, the resilient surfaces of said balls being of substantial thickness and the heavy metal core being of suflicient weight to cause the balls to flatten where the come in contact with each other during t e grinding operation, whereby the resilient surfaces have substantial surface ai'eas in contact with each other during the grinding operation.

3. The method of grinding or disintegrating vegetable or plant materials in ball mills or tube mills-which comprises subjecting the same in the presence of water to the grinding or disintegrating action of grinding balls having resilient rubber wearin surfaces and having a sufficient density to'e ect the grinding or disintegrating treatment, .the resilient surfaces of said balls being of substantial thickness and the heavy metal core being of sufficient weight to cause the balls to flatten where they come in contact with each other during the grinding operation, whereby the resilient surfaces have substantial surface areas in contact with each other during the grinding operation.

4. An improved grinding or disintegrating apparatus comprising a ball mill or tube mill having therein grinding balls having resilient rubber wearing surfaces and having a high specific gravit comparable with or greater than that of fiint pebbles, the resilient surfaces being of substantial thickness such that .the balls are flattened and have a substantial surface contact with each other during their use as grinding-elements in a ball mill.

5. An improved inding or disinte rating apparatus comprising a ball mill or tu mill having therein grinding balls made up of heavy metal cores surrounded with resilient rubber wearing surfaces, the resilient surfaces being of substantial thickness such that the balls are flattened and have a substantial surface contact with each other during their use as, grinding elements in a ball mill.-

6.- Grinding balls for use in ball mills and tube mills having resilient rubber wearing surfaces and having a s ific gravity comparable with or greater t an that of flint pebbles, the resilient surfaces being of substantial thickness such that the balls are flattened and havea substantial surface contact with each other during their use as grinding elements in a ball mill.

7. Grinding balls for use in ball mills and tube mills having resilient rubber wearin surfaces and having a metal core of high specific gravity, the resilient surfaces being of substantial thickness such that the balls are flattened and have a substantial-surface contact with each other during their use as grinding elements in a ball mill.

-. 8. Grinding or disintegrating media for ball mills or tube mills comprising a body of balls of varying sizes and diameters, the balls of each size being made up of a dense metal core and an outer resilient layer of rubber providing a resilient wearing surface for the balls, the varying diameters of the balls giving a differential surface movement of the balls during their use in ball mills or tube mills, the resilient surfaces being of substantial thickness such that the balls are flattened and have a substantial surface contact with each other during their use as grind ing elements in a ball mill.

9. An improved grinding or disintegrating apparatus comprising a ball mill or tube mill having therein a body of small balls of varying diameters provided with resilient rubber Wearing surfaces and having central cores of heavy dense metal, whereby the balls of different sizes have a differential surface motion with respect to each other during the operation of the ball mill or tube mill, the resilient surfaces being of substantial thickness such that the balls are flattened and have a sub stantial surface contact with each other during1 their use as grinding elements in a ball mi 1.

In testimony whereof I aflix my signature. GEORGE HOLMES GARNAHAN. 

